Catalyst-free room-temperature iClick reaction of molybdenum(ii) and tungsten(ii) azide complexes with electron-poor alkynes: structural preferences and kinetic studies

Two isostructural and isoelectronic group VI azide complexes of the general formula [M(η -allyl)(N )(bpy)(CO) ] with M = Mo, W and bpy = 2,2'-bipyridine were prepared and fully characterized, including X-ray structure analysis. Both reacted smoothly with electron-poor alkynes such as dimethyl a...

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Veröffentlicht in:Dalton transactions : an international journal of inorganic chemistry 2017-10, Vol.46 (39), p.13386-13396
Hauptverfasser: Schmid, Paul, Maier, Matthias, Pfeiffer, Hendrik, Belz, Anja, Henry, Lucas, Friedrich, Alexandra, Schönfeld, Fabian, Edkins, Katharina, Schatzschneider, Ulrich
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Sprache:eng
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Zusammenfassung:Two isostructural and isoelectronic group VI azide complexes of the general formula [M(η -allyl)(N )(bpy)(CO) ] with M = Mo, W and bpy = 2,2'-bipyridine were prepared and fully characterized, including X-ray structure analysis. Both reacted smoothly with electron-poor alkynes such as dimethyl acetylenedicarboxylate (DMAD) and 4,4,4-trifluoro-2-butynoic acid ethyl ester in a catalyst-free room-temperature iClick [3 + 2] cycloaddition reaction. Reaction with phenyl(trifluoromethyl)acetylene, on the other hand, did not lead to any product formation. X-ray structures of the four triazolate complexes isolated showed the monodentate ligand to be N2-coordinated in all cases, which requires a 1,2-shift of the nitrogen from the terminal azide to the triazolate cycloaddition product. On the other hand, a F NMR spectroscopic study of the reaction of the fluorinated alkyne with the tungsten azide complex at 27 °C allowed detection of the N1-coordinated intermediate. With this method, the second-order rate constant was determined as (7.3 ± 0.1) × 10 M s , which compares favorably with that of first-generation compounds such as difluorocyclooctyne (DIFO) used in the strain-promoted azide-alkyne cycloaddition (SPAAC). In contrast, the reaction of the molybdenum analogue was too fast to be studied with NMR methods. Alternatively, solution IR studies revealed pseudo-first order rate constants of 0.4 to 6.5 × 10 s , which increased in the order of Mo > W and F C-C[triple bond, length as m-dash]C-COOEt > DMAD.
ISSN:1477-9226
1477-9234
DOI:10.1039/c7dt03096g